This recipe is courtesy of Marcella Hazan. Super simple, super good.
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2 cups tomatoes, in addition to their juices (for example, a 28-ounce can of San Marzano whole peeled tomatoes)
5 tablespoons butter
1 onion, peeled and cut in half
Salt

1. Combine the tomatoes, their juices, the butter and the onion halves in a saucepan. Add a pinch or two of salt.
2. Place over medium heat and bring to a simmer. Cook, uncovered, for about 45 minutes. Stir occasionally, mashing any large pieces of tomato with a spoon. Add salt as needed.
3. Discard the onion before tossing the sauce with pasta. This recipe makes enough sauce for a pound of pasta.